Inner Ear Disorders - Neurosurgery Residentneurosurgeryresident.net/Ear. Otology/Ear36. Inner Ear Disorders.pdf · INNER EAR DISORDERS Ear36 (1) Inner Ear Disorders Last updated:

INNER EAR DISORDERS Ear36 (1)

Inner Ear Disorders Last updated: May 11, 2019

MOTION SICKNESS ................................................................................................................................... 1

MÉNIÈRE DISEASE ................................................................................................................................... 1 BENIGN PAROXYSMAL POSITIONAL VERTIGO ....................................................................................... 3

VESTIBULAR NEURONITIS ....................................................................................................................... 4 VIRAL LABYRINTHITIS ............................................................................................................................ 5

PURULENT LABYRINTHITIS ..................................................................................................................... 5 LABYRINTHITIS OSSIFICANS ................................................................................................................... 5

SUDDEN HEARING LOSS .......................................................................................................................... 5

PERILYMPHATIC (S. LABYRINTHINE) FISTULA ...................................................................................... 6 NOISE-INDUCED HEARING LOSS ............................................................................................................. 6

PRESBYCUSIS ............................................................................................................................................ 8 DRUG-INDUCED OTOTOXICITY (S. TOXIC LABYRINTHITIS) .................................................................. 8

SUPERFICIAL SIDEROSIS .......................................................................................................................... 9 HERPES ZOSTER OTICUS (s. RAMSAY HUNT SYNDROME) → see p. 256 (8) >>

TRAUMA, TEMPORAL BONE FRACTURES → see p. TrH5 >>

ACOUSTIC NEUROMA (S. ACOUSTIC SCHWANNOMA) → see p. Onc62 >>

VESTIBULAR SUPPRESSANTS, GENERAL MANAGEMENT OF VERTIGO → see p. Ear34 >>

MOTION SICKNESS

ETIOLOGY

- excessive stimulation of vestibular apparatus

individual susceptibility varies greatly.

aggravating factors: visual stimuli (e.g. moving horizon), poor ventilation (fumes, smoke, carbon

monoxide), emotional factors (e.g. fear, anxiety).

Specific forms:

1. Sea, air, car, train, swing sickness - motion (repetitive angular and linear acceleration and

deceleration) is etiologic factor.

2. Space adaptation syndrome - weightlessness (zero gravity) is etiologic factor; adaptation occurs

over several days; can recur with reentry (as gravity force increases again).

SYMPTOMS & SIGNS

- cyclic NAUSEA & VOMITING

may be preceded by: yawning, hyperventilation, salivation, pallor, profuse cold sweating, blood

pressure changes, somnolence, aerophagia, dizziness, headache, general discomfort, and fatigue.

with prolonged exposure, patient may adapt and gradually return to well-being; symptoms may

recur if motion increases or recurs after short respite.

prolonged motion sickness (with vomiting) may lead to dehydration, inanition, depression.

PROPHYLAXIS AND TREATMENT

Prevention is easier than treatment!

1) position yourself where motion is least (e.g. in middle of ship close to water level, over wings in

airplanes)

2) supine / semirecumbent position with head supported is best.

3) avoid visual fixation on waves or other moving objects, avoid reading.

4) keep axis of vision at 45° angle above horizon.

5) well-ventilated cabin is important, and going out on deck for breath of fresh air helps.

6) small amounts of fluids + simple food should be consumed frequently during extended travel; if air

travel is short, food and fluids should be avoided (alcoholic / dietary excesses before or during

travel increase likelihood of motion sickness).

7) in space adaptation syndrome, movement (which aggravates symptoms) should be avoided.

8) PROPHYLACTIC DRUGS (1 hour before departure):

DIMENHYDRINATE, DIPHENHYDRAMINE, MECLIZINE, CYCLIZINE 50 mg po,

PROMETHAZINE 25 mg po - to sedate vestibular system;

SCOPOLAMINE 0.6 mg po (dermal patch applied 4 h before departure can deliver smaller

doses - 0.5 mg over 3 days) - minimize vagal-mediated GI symptoms;

DIAZEPAM 5-10 mg po - to sedate vestibular system.

dosages should be appropriately modified for prolonged travel.

if vomiting occurs, drug must be given rectally / parenterally.

9) prolonged vomiting → i/v fluids & electrolytes.

MÉNIÈRE DISEASE

ETIOPATHOPHYSIOLOGY

- generalized dilation of membranous labyrinth (ENDOLYMPHATIC HYDROPS).

PREVALENCE ≈ 1% (≈ 50% patients have notable family history).

seen at almost all ages; typical onset begins at early-to-middle adulthood.

CAUSE unknown.

MÉNIÈRE DISEASE is idiopathic.

MÉNIÈRE SYNDROME is secondary to specific condition (e.g. endocrine abnormalities,

trauma, electrolyte imbalance, autoimmune dysfunction, medications,

infections [parasitic, syphilis], hyperlipidemia).

relative overproduction / underabsorption of endolymph → increased hydraulic pressure within

endolymphatic system.

physical distention by increased endolymphatic pressure leads to MECHANICAL DISTURBANCE of

otolithic organs (→ nonrotational vestibular symptoms) and organ of Corti (→ hearing loss and

tinnitus).

vertigo is caused by break in membrane separating perilymph (K-poor extracellular fluid) and

endolymph (K-rich intracellular fluid) → CHEMICAL MIXTURE bathes vestibular nerve receptors,

leading to depolarization blockade and transient function loss (sudden change in vestibular nerve

firing rate creates acute vestibular imbalance); symptoms improve after membrane is repaired and

normal Na and K concentrations are restored.

unilateral (≈ 20% bilateral).

CLINICAL FEATURES

Classical TETRAD:

1. Recurrent prostrating VERTIGO (usually spinning sensation, sometimes violent).

vertigo attacks appear suddenly; last for hours (up to 24 h); subside gradually.

attacks are associated with nausea & vomiting, significant nystagmus.

Direction of nystagmus is not reliable indicator of lesion site - irritative phase

during attack (fast phases toward involved ear), may be followed by paretic

phase (fast phases toward opposite ear).

vertigo is so sudden in onset and so intense that patients find themselves on floor as

if pushed by invisible force, even from sitting position (can cause devastating

accidents and falls).

INNER EAR DISORDERS Ear36 (2)

neither loss of consciousness nor other neurologic symptoms accompany fall.

anxiety and panic reactions are generated by fear that vertigo may occur at any

moment.

diagnostic tests – Romberg test, Fukuda marching step test.

2. Low-frequency sensory HEARING LOSS – fluctuates (improving between attacks!!!) but

progressively worsens over years.

3. TINNITUS (usually low-tone roaring) - constant or intermittent; may be worse before, after,

or during vertigo attack.

4. AURAL FULLNESS (feeling of discomfort, fullness, pressure in affected ear) – may be as

“warning” symptom.

disease often presents with just 1 or 2 symptoms months to years before manifesting entire tetrad.

attacks may occur in clusters and have long symptom-free remissions.

some patients are completely asymptomatic between episodes; however, many notice progressive

deterioration of hearing and balance function with each successive attack.

DIAGNOSIS

audiogram (gray shaded area indicates normal range; left ear (X marks) is normal at all

frequencies; right ear (circles) has decreased hearing on both air and bone for lower frequencies):

transtympanic electrocochleography (ECoG) can detect distortion of nerve-containing

membranes of inner ear (i.e. may suggest hydrops).

electronystagmography (ENG) with movement and caloric stimulation - endolymphatic hydrops

causes reduced vestibular response in affected ear.

Source of picture: Rudolf Probst, Gerhard Grevers, Heinrich Iro “Basic Otorhinolaryngology” (2006); Publisher: Georg Thieme Verlag;

ISBN-10: 1588903370; ISBN-13: 978-1588903372 >>

N.B. late tertiary syphilis can present with identical symptoms – always do fluorescein treponema

antibody (FTA-ABS) test!

it is conventional practice to obtain several blood tests (incl. fluorescent treponemal antibody,

antinuclear antibody, CBC, and fasting blood glucose) after diagnosing Ménière’s disease to

identify specific treatable causes.

LERMOYEZ syndrome (variant of Ménière disease) - hearing loss & tinnitus precede first vertigo

attack by months or years; hearing may improve with onset of vertigo.

TREATMENT

MEDICAL TREATMENT:

1. VESTIBULAR SUPPRESSANTS, ANTIEMETICS are useful during attacks. see p. Ear34 >>

2. Na restriction ± DIURETIC (e.g. thiazide) can prevent attacks.

3. STEROIDS (orally, intramuscularly, or even transtympanically) can reverse vertigo, tinnitus, and

hearing loss, probably by reducing endolymphatic pressure.

Combination of diuretic + vestibular suppressant controls vertigo attacks in 60-80% of patients.

Avoid in diet identifiable triggers (e.g. chocolate, caffeine, alcohol, tobacco).

SURGICAL PROCEDURES:

a) endolymphatic sac decompression (± shunting) - removing petrous bone that encases endolymph

reservoir; some surgeons insert drain or valve (from endolymphatic space to mastoid or

subarachnoid space) to further reduce pressure.

b) vestibular neurectomy relieves vertigo and usually preserves hearing.

c) labyrinthectomy - if vertigo is sufficiently disabling + hearing has degenerated to useless level;

does not require entry into cranial cavity!

d) transtympanic medication perfusion (e.g. GENTAMICIN through myringotomy) → chemical

labyrinthectomy.

e) MENIETT device - delivers pulses of pressure to inner ear via tympanostomy tube; no one knows

exactly why this works, but some patients have symptomatic relief when device is used on daily

basis.

N.B. avoid destructive procedures in bilateral Ménière disease - destruction of balance portion poses

high risk of destroying hearing as well!

After destructive procedures, patients may initially feel worse than ever!!! - vestibular rehabilitation is

helpful.

INNER EAR DISORDERS Ear36 (3)

Source of picture: Frank H. Netter “Clinical Symposia”; Ciba Pharmaceutical Company; Saunders >>

PROGNOSIS

in general, condition tends to spontaneously stabilize over time (Ménière disease is said to "burn

out" over time), but patients are left with poor balance and poor hearing.

BENIGN PAROXYSMAL POSITIONAL VERTIGO

The most common cause of true vertigo (≈ 20% vertigo patients)!

First described by Barany in 1921.

PATHOPHYSIOLOGY

Dislodged otoconia become trapped in POSTERIOR semicircular canal

INNER EAR DISORDERS Ear36 (4)

although posterior semicircular canal is most common site of lesion, patients rarely may have

horizontal or superior canal variants.

CUPULOLITHIASIS theory

granular basophilic masses composed of calcium carbonate (derived from otoliths) attached

(fixed) to CUPULA of posterior semicircular canal.

model is analogous to situation of heavy object attached to top of pole - extra weight makes pole

unstable and thus harder to keep in neutral position - pole is easily prone to "clunk" from one side

to other depending on direction it is tilted; once position is reached, weight of particles keeps

cupula from springing back to neutral.

CANALITHIASIS theory

free-moving densities (CANALITHS) in posterior semicircular CANAL.

while head is upright, particles sit at most gravity-dependent position; when head is tilted back

supine, after momentary (inertial) lag, gravity pulls particles down arc - this causes endolymph to

flow away from ampulla and causes cupula to be deflected.

model can be compared to pebbles inside tire - as tire is rolled, pebbles are picked up momentarily

and then tumble down with gravity.

ETIOLOGY

a) spontaneous degeneration of utricular otolithic membranes

b) head trauma (labyrinthine concussion)

c) otitis media

d) ear surgery

e) occlusion of anterior vestibular artery.

Rarely observed in individuals < 35 years without history of antecedent head trauma.

significant proportion of children with benign paroxysmal vertigo develop migraine headaches later

in life.

CLINICAL FEATURES

Very violent VERTIGO lasting < 30 sec (vs. in Ménière disease – lasts hours).

induced by certain head positions - lying on one ear, lying supine, rolling over in bed, tilting head

backward.

onset is typically sudden.

severity covers wide spectrum; in extreme cases, slightest head movement may be associated with

nausea and vomiting.

usually subsides in several weeks or months (but may recur after months or years).

no associated hearing loss or tinnitus!

DIAGNOSIS

Provocative pathognomonic tests – DIX-HALLPIKE maneuver, NYLEN-BÁRÁNY maneuver:

see p. D1ear >>

classic geotropic rotatory (± upbeating) nystagmus with latency, limited duration, fatigability is

pathognomonic.

sustained / nonfatiguing nystagmus may indicate CUPULOLITHIASIS rather than CANALITHIASIS.

negative test is meaningless except to indicate that active canalithiasis is not present at that

moment.

the most accurate way to define rotational nystagmus - clockwise / counterclockwise from

patient's point of view.

rotational nystagmus also can be described as geotropic / ageotropic:

Geotropic means "toward earth" and refers to upper half of eye.

Ageotropic refers to opposite movement.

– if head is turned to right, and eye rotation is clockwise from patient's point of view (top half

turns to right and toward ground), then nystagmus is geotropic.

– if head is turned toward left, then geotropic nystagmus is counterclockwise rotation.

If DIX-HALLPIKE maneuver is positive, other laboratory tests are not needed to make diagnosis!!!

Positional nystagmus may also occur with CNS lesions:

– nystagmus lacks latency, fatigability, and severe subjective sensation;

– nystagmus may continue for as long as position is maintained;

– nystagmus may be vertical or change direction, and if rotary, it is likely to be perverted

(i.e. not in anticipated direction).

TREATMENT

avoid provocative positions.

medications (such as meclizine or benzodiazepines) usually are not helpful!

most effective first choice treatment is canalith repositioning - office maneuver that shifts

particles out of semicircular canal and into vestibule, where particles do not cause symptoms.

– two modifications - EPLEY maneuver and SEMONT maneuver

– in experienced hands, success rate > 95%

if lasts for ≥ 1 year → divide nerve to posterior semicircular canal.

VESTIBULAR NEURONITIS

thought to be viral (as Bell’s palsy of CN7);

– frequent epidemics among adolescents and young adults;

– usually follows febrile illness;

– histological finding of axonal degeneration in vestibular nerve.

alternative etiology - compression by arterial loop in cerebellopontine angle.

sudden onset of severe VERTIGO (lasts for 1-2 days); self-limited.

after attack, patients may complain of unsteadiness for weeks as vestibular system gradually

accommodates.

INNER EAR DISORDERS Ear36 (5)

single episode or several attacks over 12-18 mo, with each subsequent attack being less severe and

shorter.

no associated hearing loss or tinnitus!

exclude other etiologies (e.g. tumors)

vertigo attack may be suppressed symptomatically (as in Ménière disease).

VIRAL LABYRINTHITIS

most common form of labyrinthitis; rare in children.

upper respiratory tract infection precedes onset in 50% cases.

sudden unilateral loss of VESTIBULAR FUNCTION + HEARING (vs. vestibular neuronitis)

hearing loss may be presenting symptom in many patients.

– mild to moderate (vs. purulent labyrinthitis – profound hearing loss);

– typically in high frequencies.

severe, often incapacitating, VERTIGO is characteristic (patient is often bedridden)!

– spontaneous nystagmus towards unaffected side;

– diminished / absent caloric responses in affected ear.

eventually resolves after several days to weeks; return of hearing usually mirrors return of

vestibular function (unsteadiness and positional vertigo may persist for several months).

recurrent attacks are rare (may be confused with Ménière disease).

treatment is similar to vestibular neuronitis; short course of oral corticosteroids may be helpful.

Specific Forms

Herpes zoster oticus (s. RAMSAY-HUNT syndrome) - auditory & vestibular symptoms develop in ≈

25% patients. see p. 256 (8) >>

Viral infections can cause congenital (rubella, CMV) and acquired (mumps, measles) hearing loss.

Vascular disorders (such as labyrinthine artery infarction) are generally impossible to exclude, and

their diagnosis is suggested by identical symptom complex combined with vascular risk factors.

PURULENT LABYRINTHITIS

secondary to bacterial infections:

a) ACUTE OTITIS MEDIA (via oval and round windows or dehiscent horizontal semicircular

canal [result of erosion by cholesteatoma!!!]) – typically unilateral.

b) PURULENT MENINGITIS (via cochlear aqueduct or internal auditory canal) – typically

bilateral; auditory / vestibular symptoms are present in 20% children with meningitis!

Streptococcus pneumoniae, Neisseria meningitidis are agents most likely

associated with hearing loss.

clinical features:

1) severe VERTIGO and nystagmus.

2) complete & permanent HEARING LOSS.

complications:

a) facial paralysis b) meningitis (m/o gain access to subarachnoid space through cochlear aqueduct).

c) chronic otitis media and cholesteatoma

d) labyrinthitis ossificans (decisions regarding cochlear implantation must be made early!)

cochlea, vestibule, and semicircular canals enhance on T1-weighted MRI postcontrast images in

acute labyrinthitis.

TREATMENT

- IV antibiotics appropriate for meningitis.

CEFTAZIDIME is first-line agent (reaches highest concentrations in perilymph and CSF)!

steroids in meningogenic hearing loss are controversial.

rarely - labyrinthectomy (to drain inner ear) or radical mastoidectomy.

SEROUS LABYRINTHITIS

occurs when bacterial toxins & host inflammatory mediators (cytokines, enzymes, complement)

cross round window membrane → labyrinthitis in absence of direct bacterial contamination.

associated with acute / chronic middle ear disease (one of most common complications of otitis

media!!!).

audiogram reveals mixed hearing loss when middle ear effusion is present.

vestibular symptoms are less common.

treatment - eliminating infection + clearing middle ear effusion.

LABYRINTHITIS OSSIFICANS

in various pathologies (e.g. Paget disease of bone, osteopetrosis, otosclerosis, temporal bone

trauma, inflammatory and infectious conditions, obstruction of labyrinthine artery, autoimmune

inner ear disease), new disorganized bone obliterates spaces within bony labyrinth.

Most commonly as sequela of postmeningitic purulent labyrinthitis!

mostly affected is scala tympani of basal turn.

profound deafness + loss of vestibular function.

Occurrence of ossification virtually guarantees that hearing will not be restored.

documentation of osteoneogenesis is possible with high-resolution CT (HRCT); high-resolution

T2-MRI may also be useful.

treatment – steroids + cochlear implants (timing is important determinant of successful cochlear

implantation!!! see p. Ear32 >>

SUDDEN HEARING LOSS

- unilateral severe SENSORINEURAL HEARING LOSS (> 30 dB over 3 contiguous pure-tone frequencies)

that develops over few hours.

occurs in 1 of 5000 persons every year.

bilateral in only 1-2% cases.

ETIOLOGIC CATEGORIES

1. Idiopathic - most cases.

2. Labyrinthine viral infection 3. Labyrinthine vascular compromise (embolism, thrombosis, hemorrhage); cochlea is end organ

with no collateral vasculature.

4. Intracochlear membrane ruptures 5. Immune-mediated inner ear disease - rapidly progressive, often fluctuating, bilateral hearing loss

over weeks to months (generally, too slow to classify as sudden hearing loss);

– most important diagnostic finding is improvement in hearing observed with trial of

immunosuppressants;

INNER EAR DISORDERS Ear36 (6)

– coexisting systemic autoimmune disease occurs in 15-30% of patients (RA, ulcerative

colitis, SLE, polyarteritis nodosa).

6. Tumors (internal auditory canal, cerebellopontine angle).

prognosis for some recovery of hearing is good (usually within 10-14 days).

tinnitus & vertigo may be present initially (usually subside in several days).

TREATMENT

Otologic emergency!

in idiopathic cases no form of treatment is of proven value; try:

1) bed rest.

2) corticosteroids appear rational!!!

3) vasodilators (PAPAVERINE, HISTAMINE, NICOTINIC ACID, PROCAINE, NIACIN, CARBOGEN

[5% carbon dioxide]) - improve blood supply to cochlea, reversing hypoxia.

4) rheologic agents (LOW MOLECULAR WEIGHT DEXTRANS, PENTOXIFYLLINE,

ANTICOAGULANTS) - better oxygen delivery might be achieved.

5) hyperbaric oxygen.

6) antiviral agents (ACYCLOVIR, AMANTADINE, FAMCICLOVIR, VALACYCLOVIR).

7) diuretics – used under assumption that some episodes are secondary to endolymphatic

hydrops.

8) triiodobenzoic acid derivatives (e.g. DIATRIZOATE MEGLUMINE - angiographic contrast

agent) - affect stria vascularis and assist in maintaining endocochlear potential.

PERILYMPHATIC (s. LABYRINTHINE) FISTULA

- abnormal communication between perilymphatic space and middle ear

perilymph leakage → secondary endolymphatic hydrops (as in Ménière disease).

ETIOLOGY

a) destruction of horizontal semicircular canal by CHOLESTEATOMA.

b) rupture of round / oval window membrane:

in everyday activities (lifting, straining, coughing, sneezing) increases in CSF pressure can be

transmitted to inner ear via patent cochlear aqueduct or through lamina cribrosa of internal

auditory canal → precipitous increase in pressure within INNER EAR.

pressure can increase rapidly within MIDDLE EAR as result of barometric pressure change,

scuba diving, compression trauma of ear, Valsalva maneuver, pinched-nose sneezing.

following stapedectomy

head injury!!!

c) congenital anomalies

CLINICAL FEATURES

1. Sudden severe HEARING LOSS (90%), loud roaring TINNITUS (63%), AURAL FULLNESS (25%)

patient may hear explosive sound in affected ear when fistula occurs.

2. Severe rotational incapacitating VERTIGO (≈ 80%)

DIAGNOSIS

Accurate diagnosis is difficult! – there are no reliable tests to determine presence of fistula!

Obtain gadolinium-enhanced MRI in all individuals with unilateral otologic symptoms!

Most important differential – Ménière disease!

1. FISTULA TEST (via tympanometry with electronystagmography) - application of positive pressure

to tympanic membrane produces nystagmus (nystagmus direction depends on fistula site).

2. Dynamic platform posturography: pressure is applied to external auditory canal; increase or

decrease in pressure is transmitted to tympanic membrane middle ear space and, if fistula is

present, to inner ear → abnormal sway is generated by these pressure changes; positive results give

high likelihood of having fistula.

3. Elevated SP/AP ratio on electrocochleography (ECoG)

4. Middle ear endoscopy

5. EXPLORATORY TYMPANOTOMY – definitive diagnosis!

some surgeons elect surgical exploration even when likelihood of fistula is low.

other surgeons use fairly rigid criteria.

TREATMENT

Medical therapy: sedation, bed rest, elevation of head of bed, stool softeners, avoidance of Valsalva

maneuver.

Surgical treatment

Fistula grafting is definitive treatment (highly effective for vestibular symptomatology, but its effect

on hearing loss is less predictable).

round and oval window niche must be carefully observed for accumulation of clear fluid.

β2-transferrin is specific for human aqueous humor, CSF, and perilymph; time required to

perform test prevents its intraoperative use; preoperative irrigation of middle ear via

myringotomy can obtain dilute perilymph that could be tested by Western blot analysis for

presence of β2-transferrin.

grafting is performed by removing mucosa of round and oval window area; autogenous

grafts (fascia or perichondrium) are placed directly over leak (if no actual leak is identified,

footplate and round window are grafted prophylactically).

postoperatively avoid increasing ICP (heavy lifting, straining, placing head in dependent

position).

NOISE-INDUCED HEARING LOSS

Any intense noise may damage inner ear (loss of hair cells in organ of Corti - sensory hearing loss).

a) OCCUPATIONAL NOISE-INDUCED HEARING LOSS – if noise is present in workplace.

b) SOCIOACUSIS - if noise is associated with recreational (nonoccupational) activities (mostly firearm

noise); produce minor losses because exposure times are short.

1.8% American males have handicapping NIHL.

PRESBYCUSIS is due to physiologic aging process ± lifetime of socioacusis.

PATHOPHYSIOLOGY

Hearing loss from sustained exposure

high frequencies are much more damaging than low frequencies at same physical intensity levels -

most sound level meters are equipped with filter that de-emphasizes frequencies to which human

ear is less sensitive (filter is called A filter, and measurements are reported as dBA).

INNER EAR DISORDERS Ear36 (7)

continuous stimuli are more damaging than interrupted stimuli.

any noise > 85 dB is damaging (OSHA has determined that exposure to < 85 dBA continuously for

8-hour workday is unlikely to cause harm).

changes in organ of Corti range: distorted stereocilia of inner and outer hair cells ÷ complete

absence of organ of Corti and rupture of Reissner membrane.

– OUTER HAIR CELLS are more susceptible (than inner hair cells).

– temporary threshold shifts (recover almost completely within 24 hours once noxious stimulus

is removed) are due to:

1) MECHANICAL trauma → decreased stiffness of stereocilia (floppy stereocilia respond

poorly);

2) METABOLIC exhaustion (chance of recovery, but if prolonged may cause cell death)

– permanent threshold shifts are associated with fusion of adjacent stereocilia and loss of

stereocilia.

– repeated temporary threshold shift slowly converts to permanent threshold shift

– death of sensory cell leads to Wallerian degeneration → loss of primary auditory nerve fibers.

Acoustic trauma - one-time brief exposures followed by immediate permanent hearing loss.

sound stimuli generally exceed 140 dB and are often < 0.2 seconds duration.

2 types: impulse noise (result of explosion) and impact noise (results from collision; usually metal

on metal).

MECHANICAL tearing of membranes and physical disruption of cell walls with mixing of

perilymph and endolymph; acoustic trauma can result in disruption of tympanic membrane and

ossicular injury.

CLINICAL FEATURES

persons vary greatly in susceptibility (≥ 10 years of exposure is generally required for significant

hearing loss to occur).

high-frequency tinnitus accompanies hearing loss.

symmetrical bilateral loss (permanent threshold shift) first occurs at 4 kHz (characteristic notch

centered around 4000 Hz on audiogram) → gradually occurs in higher frequencies as exposure

continues, and eventually in lower frequencies.

N.B. loss is less at 8 kHz than at 4 kHz (vs. in most sensorineural hearing losses).

– conversation on telephone is unimpaired (telephones do not use frequencies > 3 kHz).

– as severity of hearing loss increases, rate of progression decreases (provided injurious

stimulus remains constant).

– hearing loss does not progress if exposure is eliminated.

no method of treatment is available, and no recovery is expected once permanent threshold shift

has occurred.

if hearing loss interferes with communication, hearing aid is helpful.

Source of picture: Rudolf Probst, Gerhard Grevers, Heinrich Iro “Basic

Otorhinolaryngology” (2006); Georg Thieme Verlag; ISBN-13: 978-1588903372 >>

PREVENTION

1) limiting length of exposure

2) reducing noise at its source (noise levels must be monitored, either with area monitoring or

personal dosimetry).

3) ear protectors (attenuation levels 10-32 dB).

when exposure is continuous, injury is consequence of total amount of energy to which cochlear

tissues are exposed (e.g. if sound energy is doubled [i.e. increase 5 dB], risk of injury can be kept

constant if exposure time is cut roughly in half).

N.B. even brief interruptions significantly decrease amount of damage!

OSHA standard permissible exposure level (PEL):

duration of 16 hours, 85 dBA

duration of 8 hours, 90 dBA

duration of 6 hours, 92 dBA

duration of 4 hours, 95 dBA

duration of 3 hours, 97 dBA

duration of 2 hours, 100 dBA

duration of 1.5 hours, 102 dBA

duration of 1.0 hour, 105 dBA

duration of 30 minutes, 110 dBA

duration of 15 minutes, 115 dBA

- if noise levels cannot be brought down to PEL, hearing protection must be provided.

Source of picture: Rudolf Probst, Gerhard Grevers, Heinrich Iro “Basic Otorhinolaryngology” (2006); Publisher: Georg Thieme Verlag;

ISBN-10: 1588903370; ISBN-13: 978-1588903372 >>

Worker Compensation

INNER EAR DISORDERS Ear36 (8)

American Academy of Otolaryngology (committee on hearing & equilibrium) has established computational

method to determine hearing handicap:

it recognizes that hearing thresholds of 500, 1000, 2000, and 3000 Hz are critical for understanding human

conversation, and it uses only those frequencies in calculation of hearing handicap.

method also recognizes that overall hearing acuity is disproportionately determined by acuity of better-

hearing ear (calculation heavily favors better-hearing over poorer-hearing ear).

method recognizes 25-dB threshold or better to be normal.

computation is performed as follows:

o compute sum of hearing threshold levels at 500, 1000, 2000, and 3000 Hz and divide by 4;

subtract 25 from average; multiply result by 1.5 to produce percent monaural hearing

impairment.

o if monaural percent figure is same for both ears, that figure expresses percent handicap; if

percent monaural hearing impairment is different between ears, apply formula (5 x % of better

ear) + (1 x % poorer ear) divided by 6 = percent hearing handicap.

PRESBYCUSIS

- gradual bilateral sensorineural hearing loss that occurs in people as they age.

exact cause is still not known today.

related in part to lifetime noise exposure, arteriosclerosis, diabetes.

histologic changes occur throughout auditory system - from hair cells to auditory cortex:

1) thickening and secondary stiffening of basilar membrane

2) gradual cumulative epithelial atrophy (loss of hair cells)

3) atrophy of stria vascularis

4) atrophy of neurons in cochlea and central neural pathways.

Source of picture: Rudolf Probst, Gerhard Grevers, Heinrich Iro “Basic Otorhinolaryngology” (2006); Publisher: Georg Thieme Verlag;

ISBN-10: 1588903370; ISBN-13: 978-1588903372 >>

CLINICAL FEATURES

begins after age 20; becomes significant only in > 65 (25-30% people 65-74 years are impaired; for

people aged ≥ 75 years - 40-50%).

first affects highest frequencies (18-20 kHz); associated with difficulty in SPEECH DISCRIMINATION

and central auditory processing of information (esp. when background noise is present) – patients

complain that others mumble.

gradually affects lower frequencies (begins to affect 4-8 kHz range by age 55-65).

variation - some persons are severely handicapped by age 60, and some are essentially untouched

at age 90.

TREATMENT

1. Speech reading (lipreading), use of nonauditory clues.

2. Hearing aid with more gain in higher frequencies.

3. Some patients (with relatively intact spiral ganglia and central pathways) benefit from cochlear

implants.

DRUG-INDUCED OTOTOXICITY (s. TOXIC LABYRINTHITIS)

1) high-frequency sensorineural hearing loss (above 8000 Hz upper limit of standard audiogram!!!)

and high-pitched tinnitus.

2) positional nystagmus, dysequilibrium and oscillopsia.

drugs affect both auditory and vestibular portions of inner ear, but particularly toxic to organ of

Corti (cochleotoxic).

many agents produce hair cell damage.

bilaterally symmetrical, but also can be asymmetrical!

time of onset is unpredictable;

– marked hearing loss can occur even after single dose;

– hearing loss may not manifest until several months after therapy completion.

hearing loss is usually irreversible with most agents.

1. Aminoglycosides - ototoxicity is likely multifactorial (most promising mechanism involves iron

chelation leading to production of free-radical complex).

– STREPTOMYCIN, GENTAMICIN, TOBRAMYCIN are primarily vestibulotoxic.

– AMIKACIN, NEOMYCIN, KANAMYCIN, are primarily cochleotoxic

N.B. NEOMYCIN is most cochleotoxic antibiotic!

N.B. safest aminoglycoside is NETILMICIN!

2. Other antibiotics VANCOMYCIN causes reversible ototoxicity.

INNER EAR DISORDERS Ear36 (9)

ERYTHROMYCIN - sporadic cases of ototoxicity (reversible).

AZITHROMYCIN - sporadic cases of ototoxicity?

3. Salicylates (in high doses) - reversible tinnitus (!!!) and hearing loss (cochleotoxic).

4. Quinine and its synthetic substitutes - can cause reversible hearing loss (cochleotoxic).

5. Loop diuretics (ETHACRYNIC ACID, FUROSEMIDE, BUMETANIDE) – probably affect stria vascularis;

reversible cochleotoxicity.

6. Antineoplastic agents, esp. platinum-based compounds CISPLATIN > CARBOPLATIN - irreversible

severe hearing loss (cochleotoxic).

PRECAUTIONS

Avoid ototoxic drugs in:

1) renal failure - nearly all are eliminated through kidneys – monitor [drug], adjust dosage.

2) do not use as topical medication for ear when tympanic membrane is perforated (can be

absorbed into inner ear fluids).

3) pregnancy 4) elderly persons

5) persons with preexisting hearing loss.

throughout therapy, perform baseline hearing evaluations (to document preexisting hearing loss)

followed by periodic testing.

avoid noise exposure (incl. high hearing aid output) for 6 months after therapy completion.

SUPERFICIAL SIDEROSIS

- uncommon disorder caused by chronic slow or repeated bleeding into subarachnoid space.

hemosiderin deposition in subpial layers of brain and spinal cord causes parenchymal damage.

cardinal features (occur in approximately 90% of cases):

1) deafness

2) cerebellar ataxia

diagnosis:

MRI - rim of T2 hypointensity enveloping surface of brainstem, cerebellum, and

sometimes cortical fissures.

lumbar puncture - bloody / xanthochromic CSF

bleeding site goes unidentified in half the cases.

treatment – CSF leak repair (if one is present)

prognosis - progression to a bed-bound state may occur over decades in up to one-fourth of these

patients.

Axial T2-weighted (A through D) and proton density (E) brain MRI - signal hypointensity due to

hemosiderin deposition around the medulla and cerebellar vermis (A), along the cerebral convexities

(B), around the midbrain (C), around the pons and along the cerebellar folia (D), and along the

interhemispheric and sylvian fissures (E). Sagittal T1-weighted (F) and sagittal T2-weighted (G, H)

spine MRI in Cases 7 (F, H) and 15 (G), showing hemosiderin deposition along the cervical cord (F),

thoracic cord (G), and the roots of the cauda equina (H). Axial T2 (I, J) spinal MRI in Cases 15 (I) and

7 (J), showing hemosiderin deposition around the cord (I) and along the cauda, resulting in nerve root

clumping suggestive of arachnoiditis (J). Also presented is a CT showing a rim of hyperdensity due to

hemosiderin around the brainstem in Case 7 (K):

BIBLIOGRAPHY for ch. “Otology” → follow this LINK >>

Viktor’s Notes℠ for the Neurosurgery Resident

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